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Filename Latest commit message Latest commit date
Paul E. McKenney c350c00829 srcu: Prevent sdp->srcu_gp_seq_needed counter wrap
If a given CPU never happens to ever start an SRCU grace period, the
grace-period sequence counter might wrap.  If this CPU were to decide to
finally start a grace period, the state of its sdp->srcu_gp_seq_needed
might make it appear that it has already requested this grace period,
which would prevent starting the grace period.  If no other CPU ever started
a grace period again, this would look like a grace-period hang.  Even
if some other CPU took pity and started the needed grace period, the
leaf rcu_node structure's ->srcu_data_have_cbs field won't have record
of the fact that this CPU has a callback pending, which would look like
a very localized grace-period hang.

This might seem very unlikely, but SRCU grace periods can take less than
a microsecond on small systems, which means that overflow can happen
in much less than an hour on a 32-bit embedded system.  And embedded
systems are especially likely to have long-term idle CPUs.  Therefore,
it makes sense to prevent this scenario from happening.

This commit therefore scans each srcu_data structure occasionally,
with frequency controlled by the srcutree.counter_wrap_check kernel
boot parameter.  This parameter can be set to something like 255
in order to exercise the counter-wrap-prevention code.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-06-08 18:52:34 -07:00
arch Merge branch 'akpm' (patches from Andrew) 2017-06-02 15:49:46 -07:00
block block: Avoid that blk_exit_rl() triggers a use-after-free 2017-06-01 13:07:55 -06:00
certs
crypto
Documentation srcu: Prevent sdp->srcu_gp_seq_needed counter wrap 2017-06-08 18:52:34 -07:00
drivers TTY fix for 4.12-rc4 2017-06-04 11:41:41 -07:00
firmware
fs fs/ufs: Set UFS default maximum bytes per file 2017-06-04 16:33:54 -07:00
include rcu: Move rcutiny.h to new empty/true/false-function style 2017-06-08 18:52:34 -07:00
init srcu: Make SRCU be once again optional 2017-06-08 08:25:38 -07:00
ipc
kernel srcu: Prevent sdp->srcu_gp_seq_needed counter wrap 2017-06-08 18:52:34 -07:00
lib
mm mm: consider memblock reservations for deferred memory initialization sizing 2017-06-02 15:07:38 -07:00
net NFS client bugfixes for Linux 4.12 2017-06-04 11:56:53 -07:00
samples
scripts checkpatch: Remove checks for expedited grace periods 2017-06-08 08:25:27 -07:00
security
sound sound fixes for 4.12-rc4 2017-06-02 09:40:47 -07:00
tools rcutorture: Add "git diff" output to testid.txt file 2017-06-08 08:25:33 -07:00
usr initramfs: fix disabling of initramfs (and its compression) 2017-06-02 15:07:37 -07:00
virt
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS RTC for 4.12 #2 2017-06-04 11:29:32 -07:00
Makefile Linux 4.12-rc4 2017-06-04 16:47:43 -07:00
README

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.